Pergamon Tetrahedron Letters 41 (2000) 2933–2937 TETRAHEDRON LETTERS Stereocontrolled oxidation of a thiacalix[4]arene to the sulfinyl counterpart of a defined S_O configuration Naoya Morohashi, a Nobuhiko Iki, a,* Chizuko Kabuto b and Sotaro Miyano a,* a Department of Biomolecular Engineering, Graduate School of Engineering, Tohoku University, Aramaki-Aoba 07, Aoba-ku, Sendai 980-8579, Japan b Department of Chemistry, Graduate School of Science, Tohoku University, Aramaki-Aoba 07, Aoba-ku, Sendai 980-8578, Japan Received 5 January 2000; revised 15 February 2000; accepted 17 February 2000 Abstract Treatment of p-tert-butylthiacalix[4]arene (1) with benzyl bromide in THF–DMF using NaH as the base catalyst afforded the tetrabenzyl ether of cone conformation (4 C ) as the major product, oxidation of which, with NaBO 3 in CHCl 3 –acetic acid, proceeded readily to give the corresponding sulfinyl compound (5) with the four S_O groups disposed on the same side of the plane defined by the macrocyclic ring probably to avoid the steric hindrance imposed by the benzyllic moieties. Cleavage of the ether bonds gave a new stereoisomer of p-tert- butylsulfinylcalix[4]arene (2(ccc)) with the four S_O groups arranged in a cis–cis–cis configuration. © 2000 Elsevier Science Ltd. All rights reserved. Keywords: calixarenes; oxidation; sulfinyl compounds; X-ray crystallography. Since we reported the facile synthesis of p-tert-butylthiacalix[4]arene (1), 1 we have been engaged in the development of its novel functions and applications which are not attainable by the conventional methylene-bridged calix[4]arenes. 2 One of the most noteworthy features of 1 is its ability to bind various transition metal ions by virtue of the cooperative ligation of the epithio function with that of the phenoxide oxygens as revealed by solvent extraction studies and X-ray crystallography. 3,4 The well-known ready oxidizability of an epithio function to the sulfinyl and/or sulfonyl group should be another attractive feature of 1. Thus, we first showed that 1 can be selectively oxidized to either p- tert-butylsulfinylcalix[4]arene (2) or p-tert-butylsulfonylcalix[4]arene (3) by controlling the amounts of NaBO 3 as the oxidizing agent. 5 Interestingly, the direct oxidation of 1 afforded only one isomer 2(ttt) exclusively, as evidenced by NMR and X-ray crystallography, 5,6 with the four S_O groups arranged in an up–down–up–down manner to form the trans–trans–trans-isomer among the four possible combinations of the S_O configurations (Fig. 1). The stereochemical outcome of the oxidation may be ascribed to the structure of 2(ttt) which, seemingly, is the least congested and, furthermore, favored by the hydrogen * Corresponding authors. 0040-4039/00/$ - see front matter © 2000 Elsevier Science Ltd. All rights reserved. PII: S0040-4039(00)00313-0 tetl 16593